Method and apparatus for Walsh space assignment in a communication system

ABSTRACT

Techniques for Walsh space assignment are disclosed. In one aspect, a list of Walsh functions is maintained in the base station and mobile stations. A Walsh space indicator is transmitted to indicate which of the Walsh functions on the list are to be used in communication. The Walsh space indicator is updated according to the dynamically varying transmit power available or the use of Walsh functions within the base station. Methods by which a mobile station can request Walsh space information are provided. In another aspect, a Walsh space indicator channel is continually broadcast for mobile stations to detect the Walsh space indicator therefrom. In yet another aspect, the Walsh space indicator is used to initialize convolutional encoders and decoders, to provide a mechanism for mitigating against errors introduced while receiving Walsh space indicators. Various other aspects are also presented.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present Application for Patent claims priority of U.S. ProvisionalApplication No. 60/297,105, filed Jun. 7, 2001, assigned to the assigneehereof and hereby expressly incorporated by reference herein.

BACKGROUND

1. Field

The present invention relates generally to communications, and morespecifically to a novel and improved method and apparatus for Walshspace assignment in a communication system.

2. Background

Wireless communication systems are widely deployed to provide varioustypes of communication such as voice and data. These systems may bebased on code division multiple access (CDMA), time division multipleaccess (TDMA), or other modulation techniques. A CDMA system providescertain advantages over other types of systems, including increasedsystem capacity.

A CDMA system may be designed to support one or more CDMA standards suchas (1) the “TIA/EIA-95-B Mobile Station-Base Station CompatibilityStandard for Dual-Mode Wideband Spread Spectrum Cellular System” (theIS-95 standard), (2) the standard offered by a consortium named “3rdGeneration Partnership Project” (3GPP) and embodied in a set ofdocuments including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS25.213, and 3G TS 25.214 (the W-CDMA standard), (3) the standard offeredby a consortium named “3rd Generation Partnership Project 2” (3GPP2) andembodied in “TR-45.5 Physical Layer Standard for cdma2000 SpreadSpectrum Systems” (the IS-2000 standard), and (4) some other standards.

In the above named standards, the available spectrum is sharedsimultaneously among a number of users, and techniques such as softhandoff are employed to maintain sufficient quality to supportdelay-sensitive services, such as voice. Data services are alsoavailable. More recently, systems have been proposed that enhance thecapacity for data services by using higher order modulation, very fastfeedback of Carrier to Interference ratio (C/I) from the mobile station,very fast scheduling, and scheduling for services that have more relaxeddelay requirements. An example of such a data-only communication systemusing these techniques, is the high data rate (HDR) system that conformsto the TIA/EIA/IS-856 standard (the IS-856 standard).

In contrast to the other above named standards, an IS-856 system usesthe entire spectrum available in each cell to transmit data to a singleuser at one time, selected based on link quality. In so doing, thesystem spends a greater percentage of time sending data at higher rateswhen the channel is good, and thereby avoids committing resources tosupport transmission at inefficient rates. The net effect is higher datacapacity, higher peak data rates, and higher average throughput.

Systems can incorporate support for delay-sensitive data, such as voicechannels or data channels supported in the IS-2000 standard, along withsupport for packet data services such as those described in the IS-856standard. One such system is described in a proposal submitted by LGElectronics, LSI Logic, Lucent Technologies, Nortel Networks, QUALCOMMIncorporated, and Samsung to the 3rd Generation Partnership Project 2(3GPP2). The proposal is detailed in documents entitled “Updated JointPhysical Layer Proposal for 1xEV-DV”, submitted to 3GPP2 as documentnumber C50-20010611-009, Jun. 11, 2001; “Results of L3NQS SimulationStudy”, submitted to 3GPP2 as document number C50-20010820-011, Aug. 20,2001; and “System Simulation Results for the L3NQS Framework Proposalfor cdma2000 1x-EVDV”, submitted to 3GPP2 as document numberC50-20010820-012, Aug. 20, 2001. These are hereinafter referred to asthe 1xEV-DV proposal.

A system such as the one described in the 1xEV-DV proposal generallycomprises channels of four classes: overhead channels, dynamicallyvarying IS-95 and IS-2000 channels, a forward packet data channel(F-PDCH), and some spare channels. The overhead channel assignments varyslowly, they may not change for months. They are typically changed whenthere are major network configuration changes. The dynamically varyingIS-95 and IS-2000 channels are allocated on a per call basis or are usedfor IS-95, or IS-2000 Release 0 through B packet services. Typically,the available base station power remaining after the overhead channelsand dynamically varying channels have been assigned is allocated to theF-PDCH for remaining data services. The F-PDCH is typically used fordata services that are less sensitive to delay while the IS-2000channels are used for more delay-sensitive services.

The F-PDCH, similar to the traffic channel in the IS-856 standard, isused to send data at the highest supportable data rate to one user ineach cell at a time. In IS-856, the entire power of the base station andthe entire space of Walsh functions are available when transmitting datato a mobile station. However, in the proposed 1xEV-DV system, some basestation power and some of the Walsh functions are allocated to overheadchannels and existing IS-95 and cdma2000 services. The data rate that issupportable depends primarily upon the available power and Walsh codesafter the power and Walsh codes for the overhead, IS-95, and IS-2000channels have been assigned. The data transmitted on the F-PDCH isspread using one or more Walsh codes.

In the proposed scheme, the base station only transmits to one mobilestation on the F-PDCH at a time, although many users may be using packetservices in a cell. Mobile stations are selected for forward linktransmission based upon some scheduling algorithm. One such algorithm isdisclosed in U.S. patent application Ser. No. 08/798,951, entitled“METHOD AND APPARATUS FOR FORWARD LINK RATE SCHEDULING”, filed Feb. 11,1997, assigned to the assignee of the present invention.

Due to the bursty nature of packet data, some users' data connectionsmay not be active. These mobile stations enter a state known as thedormant state in many of the CDMA standards (see TIA/EIA/IS-707, DataService Options for Spread Spectrum Systems). When the mobile or basestation has data to send, signaling is used to place the mobile stationonto the traffic channel. From time to time, users may move out of orinto the cell, and others may initiate or terminate their connection.Each mobile station, to receive data on the F-PDCH, must have the Walshcodes, also referred to as the Walsh space, being used for the F-PDCH,also. Since the Walsh space will tend to vary dynamically with time andmay vary between cells (or sectors within a cell), Walsh spaceinformation will need to be relayed to the various users within eachcell, including mobile stations coming out of the dormant state. Thereis therefore a need in the art for Walsh space assignment thateffectively distributes the Walsh space to the various users whileminimizing the use of system resources for its distribution.

SUMMARY

Embodiments disclosed herein address the need for Walsh space assignmentthat effectively distributes the Walsh space to the various users whileminimizing the use of system resources for its distribution. In oneaspect, a list of Walsh functions is maintained in the base station andmobile stations. A Walsh space indicator is transmitted to indicatewhich of the Walsh functions on the list are to be used incommunication. The Walsh space indicator is updated according to thedynamically varying transmit power available or the use of Walshfunctions within the base station. Methods by which a mobile station canrequest Walsh space information are provided. In another aspect, a Walshspace indicator channel is continually broadcast for mobile stations todetect the Walsh space indicator therefrom. In yet another aspect, theWalsh space indicator is used to initialize convolutional encoders anddecoders, to provide a mechanism for mitigating against errorsintroduced while receiving Walsh space indicators. Various other aspectsare also presented.

The invention provides methods and system elements that implementvarious aspects, embodiments, and features of the invention, asdescribed in further detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 is a wireless communication system that supports a number ofusers, and which can implement various aspects of the invention;

FIG. 2 depicts an exemplary base station;

FIG. 3 depicts an exemplary mobile station;

FIG. 4 is a flowchart depicting an embodiment of a method oftransmitting a Walsh space indicator;

FIG. 5 is a flowchart of an embodiment of a method of optionallyincluding a Walsh space indicator in another message packet;

FIG. 6 depicts one method by which a mobile station can convey a needfor Walsh space information to a base station;

FIG. 7 depicts an alternate method by which a mobile station can conveya need for Walsh space information to a base station;

FIG. 8 depicts yet another alternate method by which a mobile stationcan convey a need for Walsh space information to a base station;

FIG. 9 shows the timing relationship between a transmission ofWALSH_SPACE on the F-WICH and the use of that WALSH_SPACE on the F-PDCH;

FIG. 10 is a flowchart of an embodiment of a method of receiving theF-WICH;

FIG. 11 is a flowchart of an embodiment of a method of receiving theF-WICH and using convolutional decoder initialization as an interlockfor mitigating errors received on the F-WICH; and

FIG. 12 is a flowchart depicting an embodiment of a method of conveyingthe Walsh space information during handoff.

DETAILED DESCRIPTION

FIG. 1 is a diagram of a wireless communication system 100 that supportsa number of users, and can implement various aspects of the invention.System 100 may be designed to support one or more CDMA standards and/ordesigns (e.g., the W-CDMA standard, the IS-95 standard, the IS-2000standard, the IS-856 standard, the 1xEV-DV proposal). For simplicity,system 100 is shown to include three base stations 104 in communicationwith two mobile stations 106. The base station and its coverage area areoften collectively referred to as a “cell”. In IS-95 systems, a cell mayinclude one or more sectors. In the W-CDMA specification, each sector ofa base station and the sector's coverage area is referred to as a cell.As used herein, the term base station can be used interchangeably withthe term access point. The term mobile station can be usedinterchangeably with the terms user equipment (UE), subscriber unit,subscriber station, access terminal, remote terminal, or othercorresponding terms known in the art. The term mobile stationencompasses fixed wireless applications.

Depending on the CDMA system being implemented, each mobile station 106may communicate with one (or possibly more) base stations 104 on theforward link at any given moment, and may communicate with one or morebase stations on the reverse link depending on whether or not the mobilestation is in soft handoff. The forward link (i.e., downlink) refers totransmission from the base station to the mobile station, and thereverse link (i.e., uplink) refers to transmission from the mobilestation to the base station.

For clarity, the examples used in describing this invention may assumebase stations as the originator of signals and mobile stations asreceivers and acquirers of those signals, i.e. signals on the forwardlink. Those skilled in the art will understand that mobile stations aswell as base stations can be equipped to transmit data as describedherein and the aspects of the present invention apply in thosesituations as well. The word “exemplary” is used exclusively herein tomean “serving as an example, instance, or illustration.” Any embodimentdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other embodiments.

A common application for communication system 100 is to provide packetdata service for mobiles, including a connection to the Internet. A basestation 104 may comprise one or more base station transceiver subsystems(BTS), connected to a base station controller (BSC). A Packet DataService Node (PDSN), used to send data to and receive data from anetwork, such as the Internet, connects to the BSC within one or morebase stations to provide packet services to the mobile stations incommunication therewith via on or more BTSs. Various protocols forpacket data are known in the art and can be applied at the appropriatelocations throughout communication system 100. These details are notshown in FIG. 1.

As described above, a system such as that described in the 1xEV-DVproposal uses the remaining transmit power, after power has beenallocated to support existing channels such as voice, to transmit at thehighest rate supportable to a single mobile station at a time. A 1xEV-DVsystem may also transmit to multiple mobile stations at the same time, amode that is also supported within the scope of the present invention.The data channel for forward transmission is referred to as the ForwardPacket Data Channel (F-PDCH). The choice of mobile station fortransmission is based in large part on channel quality indicators, whichare transmitted to the base station by each mobile station with a packetdata connection. The channel quality indicator messages are sent to thebase station on a channel referred to as the Reverse Channel QualityIndicator Channel (R-CQICH). The base station will avoid sending to amobile station that is experiencing poor channel quality at the time,opting instead to send at high rate to another mobile station, returningto the first after the channel quality improves.

The base station uses one or more control channels in association withthe forward data channel. One such channel is the Forward Primary PacketData Control Channel (F-PPDCCH), another is the Forward Secondary PacketData Control Channel (F-SPDCCH). Control channels can be used to conveybroadcast information to all the mobiles, or targeted messages to asingle mobile. A control message may indicate which mobile is to receivethe data on the F-PDCH, the rate, the number of packets, and similarinformation.

A send and re-transmit protocol can be established to ensure packetsdestined for mobile stations arrive as transmitted. A mobile stationsends an acknowledgement to the base station when it receives a packeton the forward data channel. This acknowledgement can be sent on theReverse Acknowledgement Channel (R-ACKCH). If an acknowledgement failsto arrive from a mobile station after the base station transmits to it,the base station can re-transmit the packet. In the exemplaryembodiment, the base station will attempt to re-transmit a packet fourtimes.

The mobile stations can also transmit data to the base station on thereverse link. One channel for reverse link data transmission is referredto as the Reverse Supplemental Channel (R-SCH). A reverse link controlchannel is used to indicate the rate data is transmitted on the R-SCH,referred to as the Reverse Rate Indicator Channel (R-RICH).

Data transmitted on the forward data channel, or F-PDCH, may be spreadusing one or more Walsh codes. In the exemplary embodiment, the data maybe covered using up to 28 Walsh codes. As described above, the amount oftransmission power available for F-PDCH transmission, and the number ofWalsh channels needed, varies as the number of voice and other datachannels varies. It is necessary for the base station to communicate tothe mobile stations the number of Walsh channels being used duringupcoming transmissions, which Walsh channels they are, and the orderthat the data will be modulated on the Walsh channels. This collectiveset of information can be referred to as the Walsh space.

FIG. 2 depicts an exemplary base station 104. For clarity, only a subsetof the components relating to this description are shown. Forward linksignals are transmitted from and reverse link signals are received onantenna 210. The forward link signals are generated in transmitter 250,which is shown communicatively coupled with encoder 260. Transmitter 250may process data for transmission using a variety of techniques, knownin the art. Examples of such processing include Walsh Covering,pseudo-random noise (PN) spreading, interleaving, encoding,radio-frequency (RF) processing such as up-conversion and carriermodulation, and the like. When transmitting data on the F-PDCH,transmitter 250 covers the appropriate data symbols with thecorresponding Walsh functions as defined in the current Walsh space.Encoder 260 may be included as part of transmitter 250, but is shown asa separate element in FIG. 2 for clarity of discussion below. Encoder260 can employ various encoding schemes, examples include CyclicRedundancy Check (CRC) encoding, convolutional or block encoding, turboencoding, and the like. Among other data that can be transmitted on theforward link via transmitter 250 and antenna 210, for example, packetdata, as described above with respect to FIG. 1, are messages generatedin message generator 240. Messages generated in message generator 240may be control messages for transmission on the F-PPDCH or the F-SPDCCH,which are processed and transmitted in transmitter 250.

Reverse link signals are delivered from antenna 210 to receiver 220,where various processing, known in the art, is used to retrieve datafrom the reverse link signals. Examples of the processing that can beperformed in receiver 220 include amplification, RF down-conversion,demodulation (including PN despreading and Walsh decovering), combining,deinterleaving, decoding, and the like.

Data from receiver 220 may have various destinations, one of which isshown as message decoder 230. Message decoder 230 can decode variousmessages sent from one or more mobile stations, such as those reverselink messages described above. Message generator 240 is responsive tomessage decoder 230, in that some forward link messages are generated inresponse to information carried in reverse link messages. Examples ofthis will be detailed in various embodiments below. Note that a typicalbase station may include a central processing unit (CPU) or digitalsignal processor (DSP) for interconnecting and managing the variousfunctional blocks described (CPU or DSP not shown). In fact, the variousblocks of FIG. 2, including the message generator 240 and messagedecoder 230, may be processes running on a CPU or DSP. The functionalblocks shown are for clarity of discussion only, as those skilled in theart will recognize the myriad ways of implementing the blocks describedherein in special purpose hardware, CPU or DSP, or combinations thereof,all within the scope of the present invention. The communicative linkbetween the message decoder 230 and the message generator 240 mayinclude various blocks not shown, such as the aforementioned CPU or DSP.

FIG. 3 depicts an exemplary mobile station 106. For clarity, only asubset of the components relating to this description are shown. Reverselink signals are transmitted from and forward link signals are receivedon antenna 310. The reverse link signals are generated in transmitter350. Transmitter 350 may process data for transmission using a varietyof techniques, known in the art. Examples of such processing includeWalsh Covering, pseudo-random noise (PN) spreading, interleaving,encoding, radio-frequency (RF) processing such as up-conversion andcarrier modulation, and the like. Among other data that can betransmitted on the reverse link via transmitter 350 and antenna 310 aremessages generated in message generator 340. Messages generated inmessage generator 340 may be control messages such as channel quality,acknowledgement, rate information and the like. Examples include theR-CQICH, R-ACKCH, and the R-RICH, each of which are processed andtransmitted in transmitter 350.

Forward link signals are delivered from antenna 310 to receiver 320,where various processing, known in the art, is used to retrieve datafrom the forward link signals. Examples of the processing that can beperformed in receiver 320 include amplification, RF down-conversion,demodulation (including PN despreading and Walsh decovering), combining,deinterleaving, decoding, and the like. Decoder 360 is showncommunicatively coupled to receiver 320. Decoder 360 may be included aspart of receiver 320, but is shown as a separate element in FIG. 3 forclarity of discussion below. Decoder 360 may decode according to one ormore of a variety of decoding schemes known in the art. Examples includeCRC decoders, convolutional decoders, turbo decoders, and the like. Whenreceiving data on the F-PDCH, receiver 320 decovers the appropriate datasymbols with the corresponding Walsh functions as defined in the currentWalsh space.

Data from receiver 320 may have various destinations, one of which isshown as message decoder 330. Message decoder 330 can decode variousmessages sent from one or more base stations, such as the forward linkmessages described above. Message generator 340 is responsive to messagedecoder 330, in that some reverse link messages are generated inresponse to information carried in forward link messages. Examples ofthis will be detailed in various embodiments below. Note that a typicalmobile station may include a central processing unit (CPU) or digitalsignal processor (DSP) for interconnecting and managing the variousfunctional blocks described (CPU or DSP not shown). In fact, the variousblocks of FIG. 3, including the message generator 340 and messagedecoder 330, may be processes running on a CPU or DSP. The functionalblocks shown are for clarity of discussion only, as those skilled in theart will recognize the myriad ways of implementing the blocks describedherein in special purpose hardware, CPU or DSP, or combinations thereof,all within the scope of the present invention. The communicative linkbetween the message decoder 330 and the message generator 340 mayinclude various blocks not shown, such as the aforementioned CPU or DSP.

FIG. 4 depicts a flowchart of an embodiment of a method forcommunicating Walsh space information to mobile stations. A message issent on a broadcast channel, referred to as a Forward Broadcast ControlChannel (F-BCCH) containing the Walsh numbers and the number of channelsfor various forward channels, including the F-PPDCCH, the F-SPDCCH, andthe F-PDCH. In the exemplary embodiment, the F-PDCH may use up to 28Walsh functions. The list of functions for use in transmission andreception of the F-PDCH is referred to herein as the Walsh list. In analternative embodiment, a default list is used in lieu of transmissionof the Walsh list on the F-BCCH. An example of a Walsh list is shown inTable 1. In this example, the Walsh functions to be used are 31, 15, 30,14, and so on. In addition to the Walsh list, the base station and themobile stations need to agree on the order in which symbols are appliedto the various Walsh functions, so as to facilitate proper decoding. Onesolution is to use the order of the Walsh list, although any method ofselecting the Walsh functions falls within the scope of the presentinvention. Whether a default list is used is shown as decision block 410in FIG. 4. If not, then proceed to block 420 and broadcast the Walshspace list. If a default modulation order, such as the order of theWalsh list, is not specified, that modulation order can be specified bybroadcasting the modulation order, also in block 410.

TABLE 1 Default Walsh Space for F-PDCH (in 32 Space) 31 15 30 14 29 1328 12 27 11 26 10 25  9 24  8 23  7 22  6 21  5 20  4 19  3 18  2

Once the overall Walsh space is defined, the sub-space to be used forany particular transmission on the F-PDCH can be indicated by a singlenumber, referred to herein as a Walsh space indicator, or WALSH_SPACE.The Walsh space indicator specifies how many Walsh functions are to beused. The Walsh list, and associated modulation order, can then be usedwith the Walsh space indicator to identify the Walsh functions for usein data communication. An example Walsh sub-space corresponding toWALSH_SPACE equal to six is shown in Table 2. In this example six Walshfunctions will be used, and they will be 31, 15, 30, 14, 29, and 13, inthat order. The Walsh space must be transmitted initially to all mobilestations in block 430. Whenever the Walsh space changes, the Walsh spaceindicator must be sent to identify the new Walsh space. This is shown inFIG. 4 in decision block 440, where the flow loops back to decisionblock 440 when the Walsh space has not changed, but proceeds to block430 to send the Walsh space indicator when it has changed.

TABLE 2 Example Walsh Space WALSH_SPACE = 6 31 15 30 14 29 13

Any number of different tables can be supported within the scope of thepresent invention. Table 3 shows an alternate default Walsh Space,suitable as a default Walsh list for allocation of Walsh channels duringtransmission of data on a channel such as the F-PDCH.

TABLE 3 Alternative Default Walsh Space for F-PDCH (in 32 Space) 31 1523 7 27 11 19 3 29 13 21 5 25 9 30 14 22 6 26 10 18 2 28 12 20 4 24 8

In the exemplary embodiment, the Walsh Space Indicator is sent in amessage, an example of which is shown in Table 4. In this example, themessage has 13 information bits with 6 bits allocated to the multipleaccess control identifier (MAC-ID), and 7 bits used to signal the packetstructure. In the exemplary embodiment, a MAC-ID of 0 indicates control,which can be used to broadcast to all the mobiles monitoring that basestation's transmissions. Of the remaining 7 bits, two are used toindicate the type of information and the remaining 5 bits indicate thenumber of Walsh functions being used. In this example, CON_INFO_TYPE canbe used to indicate that the message contains a Walsh space indicator.WALSH_SPACE is a 5-bit number indicating the number of Walsh functionsbeing used. The message can be sent on a control channel. In theexemplary embodiment, the Walsh Space Indicator message can be sent onthe F-SPDCCH.

TABLE 4 Field Length (bits) Value MAC_ID 6 000000 CON_INFO_TYPE 2WALSH_SPACE 5

In the 1xEV-DV proposal, messages on the control channel, such as theF-SPDCCH can be transmitted using 1, 2, or 4 slot packets. When the8-slot F-PDCH format is used, a 4-slot F-SPDCCH format is used. Thus, itis possible to use the remaining 4 slots to transmit the WALSH SPACE ina 4-slot F-SPDCCH message. If no 8-slot F-PDCH transmissions are beingused, a Walsh Space Indicator message may need to be sent on theF-SPDCCH, using some forward link capacity.

A flowchart depicting an embodiment of this method is shown in FIG. 5.The flow loops back from decision block 510 to itself when a Walshupdate is not required. When a Walsh update is required, proceed todecision block 520, to determine if there is time when the F-PDCH isbeing transmitted but a control message is not being transmitted. If so,proceed to block 530 and transmit the Walsh space indicator messageusing the spare control message. If not, proceed to block 540 andtransmit the Walsh space indicator using a dedicated control message.

One of the situations in which the percentage of 8-slot packets is lowoccurs when the channel is being used for data only operation (all 28 ofthe Walsh codes are available). In this situation, a change in the Walshspace may require a special transmission of the Walsh Space Indicatormessage on the control channel, reducing overall system capacity.However, in situations such as this, the Walsh space is not changingdramatically, so the effect on overall system capacity is minimal.

The Walsh space may change more dynamically when some of the channel isallocated for voice or services other than F-PDCH services. In thiscase, a greater fraction of 8-slot transmissions will be available sincethe amount of available power is less.

In general, every time the base station changes the Walsh space, theWalsh Space Indicator should be transmitted. In the exemplaryembodiment, the Walsh space information can be sent to the mobilestation during call setup using the Extended Channel Assignment Message(ECAM), defined in the IS-2000 standard. If the Walsh space changessubsequently, the base station can update the mobile station using theF-SPDCCH message with the Walsh Space Indicator.

In addition, there may be circumstances in which the mobile station maywant to communicate a need for the Walsh space information to the basestation. For example, a mobile station may need to be updated with theWalsh space information when it hands off or requests that F-PDCHtransmissions occur from a new cell or sector. There are a variety oftechniques the mobile station can employ to convey this need to the basestation.

In one embodiment, depicted in FIG. 6, the mobile needs Walsh spaceinformation, as shown in step 610. The mobile conveys this to the basestation by not transmitting the reverse quality indicator, for examplethe R-CQICH. If the base station does not receive the R-CQICH, then itdoes not transmit data to the mobile station, but can instead transmitthe Walsh space information. In an alternative embodiment, shown in FIG.7, the mobile responds to the need for Walsh space information, step710, by sending a special value on the R-CQICH, one not used for regularoperation, for example. This latter arrangement is useful whentransmissions from the mobile station are sometimes not received.

Either of these methods can be used to trigger the base station to sendthe Walsh space information on the forward link. Using the alternativemethod, shown in FIG. 7, the special value on the R-CQICH can be used tofacilitate updating the Walsh space information during a handoff or whenrequesting that a cell or sector already in the active set transmit tothe mobile station. The R-CQICH contains carrier-to-interference (C/I)information corresponding to a specific base station. A mobile station,subsequent to handoff, can send this special value with the new basestation indication, and the base station knows that it needs to send theWalsh space information. A system using Walsh covering of C/I messagesto direct the messages to a particular base station is disclosed incopending U.S. patent application Ser. No. 08/963,386, entitled “METHODAND APPARATUS FOR HIGHER RATE PACKET DATA TRANSMISSION”, filed Nov. 3,1997, and assigned to the assignee of the present invention.

FIG. 8 depicts yet another method for communicating a need for Walshspace information, shown in step 810. In step 820, the mobile sends achannel quality indicator, on the R-CQICH, for example, in the normalfashion. In step 830, a special value is sent on one of the otherreverse control channels. For example, a value on the rate indicatorchannel, such as the R-RICH, can be used which isn't otherwise used toindicate a valid rate. Alternatively, a special value can be sent on anacknowledgement channel, such as the R-ACKCH. Another way would be tohave a special channel just for this function. By using another channel,the base station obtains channel quality indicator information from themobile station and thus allows the base station to use the channelquality indicator information to select a time to transmit the Walshspace information when the channel is good. This increases thelikelihood that the mobile station will accurately receive theinformation, reduces the amount of power to transmit the Walsh spaceinformation, or both.

In order to determine the probability of error for receiving the Walshspace information when channel quality feedback from the mobile stationis not used, long term fading statistics can be used. As an example, fora 1% forward error rate (FER), the control channel requires at worst 18dB E_(b)/N_(t) (energy per bit/thermal noise), at approximately 30 km/hrin a 1-path Rayleigh fading environment. The required E_(c)/I_(or)(energy per chip/total transmitted energy from the base station) isgiven by:

$\begin{matrix}{\frac{E_{c}}{I_{or}} = {\left( \frac{E_{b}}{N_{t}} \right)\left( \frac{R}{W} \right)\left( \frac{1}{G} \right)}} & {{Equation}\mspace{14mu} 1}\end{matrix}$where R is the data rate, W is the transmission bandwidth, and G is thegeometry (ratio of power from cell the mobile station is monitoring toall other cells), in dB. A message contains 29 bits, thus the requiredE_(c)/I_(or) for a 1-slot case is 0.7 dB—G. It is clear that there isinsufficient power for detection near the cell edge (G is 0 dB or less).However, if the Walsh space information is repeated, and a 1% FER isdesired after two repeats (and assuming fading is independent betweenrepeats), then the required E_(b)/N_(t) is about 8 dB and the requiredE_(c)/I_(or) for a 1-slot case is −10.3 dB—G. The total energy, in termsof E_(c)/I_(or), is −7.3—G. Thus, by using a relatively large portion ofthe channel power, the Walsh space indication can be reliablytransmitted to the mobile station. Alternative embodiments, which do notrequire such a large portion of the channel power for reliabletransmission are discussed below.

An alternative method for communicating the Walsh space information isto use a continuously transmitted code division multiplexed channel.This channel will be referred to herein as the Forward Walsh IndicatorChannel, or F-WICH. Using this method has the benefits of allowing theWalsh space to be transmitted at lower power. The mobile station cancombine energy from the repetition of the Walsh space information. Thetime diversity introduced by repeating the information can smooth overfading processes. Furthermore, mobile stations do not need to convey aneed for the Walsh space information to the base station, since theinformation is being continuously broadcast.

In the exemplary embodiment, a 20 ms frame and a length 256 Walshfunction can be used for the F-WICH. There will be 96 available symbolsper frame. A simple block code can be used, such as a (24, 7) coderepeated four times, similar to that used for the R-RICH, as defined inthe 1xEV-DV proposal.

The base station continually sends the F-WICH. When the Walsh spacechanges, the base station transmits the new Walsh Space Indicator oneframe plus several (e.g., two) slots in advance of the actual change onthe air. In the context of the IS-95 and cdma2000 air interfaces, a slotis equal in duration to a power control group, the length of both being1.25 ms. FIG. 9 shows this relative timing. WALSH_SPACE is transmittedon the F-WICH. 20 ms plus some number (e.g., two) slots later the 16slots corresponding to the updated WALSH_SPACE are transmitted on theF-PDCH.

The mobile station decodes the F-WICH every frame. If the F-WICH is notreceived correctly, there are a variety of strategies that the mobilestation can use. One is to assume the previous value of WALSH_SPACE,which is useful if the WALSH_SPACE does not change very frequently. Asecond is to just wait for the new F-WICH transmission. Othertechniques, such as those described above in relation to FIGS. 6-8 thatcan be used by the mobile station to let the base station know. While,as stated above, it is not necessary for the base station to know thatthe mobile station did not receive the Walsh information correctly,because that information is continuously being transmitted, there areother considerations which may make such communication useful.

For example, in the 1xEV-DV proposal, a retransmission scheme is usedsuch that a packet may be delivered to a mobile station up to fourtimes, waiting for an acknowledgement of the packet. If the mobilestation does not have the correct Walsh space, then all fourtransmissions will most likely be received in error (even if the channelwas good during the transmissions). An upper layer retransmissionprotocol (e.g., RLP) will correctly handle this situation, but systemresources and capacity are squandered while transmitting to a mobilestation incapable of receiving. So a base station may wish to receive anindication from a mobile station that the Walsh space was not received,so to avoid transmitting until the mobile station will be able toreceive once again. The mobile station can communicate this by nottransmitting the channel quality indicator, such as the R-CQICH as isshown in FIG. 6. Or, a special value of the channel quality indicatorcan be transmitted as is shown in FIG. 7. Other alternate reversechannels can also be used to indicate the lack of valid Walsh spacedecoding by the mobile station, such as the reverse rate indicator, orR-RICH, or the acknowledgment channel, or R-ACKCH.

If the mobile station does not correctly receive the Walsh spaceindicator on the F-WICH in one frame, it can combine the code symbolsthat were received in the previous frame with those in the currentframe. This provides an additional 3 dB of energy for decoding the Walshspace indicator. However, if the Walsh space indicator changed from onetransmission to the next, then there is a high likelihood that thetransmission would not be decoded. Thus, one would likely use this typeof approach when the Walsh space indicator does not change very often.

A flowchart depicting an exemplary embodiment of a method for sendingand receiving the F-WICH is shown in FIG. 10. Block 1010 indicates thatthe base station continuously transmits the F-WICH. Proceed to block1020, where the mobile station receives the next frame of the F-WICH.Proceed to decision block 1030. If, in decision block 1030, the F-WICHwas decoded correctly, proceed to block 1040 to transmit the reversechannel quality indicator, on the R-CQICH, for example. Proceed back toblock 1020 to receive the next frame.

If, in decision block 1030, the F-WICH was not decoded correctly,proceed to block 1050, and combine the symbols from the frame with thesymbols from the previous frame. Proceed to decision block 1060. Indecision block 1060, if the F-WICH is decoded correctly from thecombined symbols, proceed to block 1040 and transmit the reverse channelquality indicator, as described above. If the combined symbols do notdecode correctly, proceed to block 1020 to receive the next frame, asdescribed above, or proceed to optional block 1070 (shown in dashedoutline), to notify the base station that the F-WICH was not receivedcorrectly. Various methods for notifying the base station have beendescribed above, including refraining from transmitting the reversechannel quality indicator, sending a special channel quality indicatorvalue, sending a special value on another reverse channel, and the like.From block 1070, proceed to block 1020 to receive the next frame. Table6 outlines the various possible outcomes using somewhat differentdecision rules, using decoding results for two sequential frames,labeled i-1 and i.

An alternative embodiment, using a separate code division multiplexedchannel, such as the F-WICH, can be used to mitigate the problemsassociated with a mobile station receiving an incorrect WALSH_SPACEvalue on the F-WICH. In one embodiment, a cyclic redundancy check (CRC)encoder in the base station and mobile station are initialized using thecurrent value of WALSH_SPACE. For example, encoder 260 in the basestation and decoder 360 in the mobile station can be used to calculatethe appropriate CRC. If the mobile station has not updated its versionof WALSH-SPACE correctly when the base station has changed it, it isvery unlikely that the packet header will be correctly decoded on theF-SPDCCH. As a result, the mobile station will not receive thesub-packet for that transmission. As one possible alternative, theinitial state of the error correcting encoder (e.g., convolutionalencoder) in the base station (260) and the mobile station (360) areinitialized using the current value of WALSH_SPACE. It should beunderstood, that other rules described here (such as those given in FIG.10 or Table 6) can also be used with this alternative embodiment.

TABLE 6 Outcome for frame i-1 Outcome for frame i Action to be takenGood Good Use WALSH_SPACE from frame i. Bad Good Use WALSH_SPACE fromframe i. Good Bad Use WALSH_SPACE from frame i-1 (note that the F-SPDCCHheader will not likely be decoded correctly if WALSH_SPACE has changed.Bad Bad Combine energy from both frame i-1 and frame i. If it decodesproperly, then use WALSH_SPACE from the combined frames. If not, use thelast previously available WALSH_SPACE. Again, the F-SPDCCH header willnot likely be decoded correctly if WALSH_SPACE has changed.

As before, if the mobile station does not have the correct WALSH_SPACEindication, perhaps due to handoff, or errors received in an update onthe F-WICH, the mobile station can alert the base station using any ofthe techniques, such as those discussed above with relation to FIGS.6-8. The base station can then avoid sending data to that mobile stationuntil it has correctly received the WALSH_SPACE. This avoids wastingsystem resources by transmitting data to a mobile station incapable ofcorrectly receiving it.

FIG. 11 depicts a flowchart of an embodiment of the method justdescribed. The mobile station receives frame i in block 1110. Proceed todecision block 1115 to determine if frame i decoded correctly. If so,use the WALSH_SPACE included in frame i. Initialize the decoder withWALSH_SPACE in block 1160, decode the data control channel in block1165, increment i in block 1170, proceed to receive the next frame i inblock 1110, and repeat the process.

If frame i did not decode correctly in decision block 1115, proceed todecision block 1125 to determine if the prior frame, i−1, decodedcorrectly. If so, proceed to block 1155 and use the WALSH_SPACE from theprior frame. There is no need to combine the frames, because if theWalsh space has not changed, the prior value of WALSH_SPACE is valid,and if it has changed, combining the two different values will likely bein error anyway. If the Walsh space has changed, then the controlchannel will very likely not be decodable since the decoderinitialization will not be current. Initialize the decoder withWALSH_SPACE in block 1160, decode the data control channel in block1165, increment i in block 1170, proceed to receive the next frame i inblock 1110, and repeat the process.

If, in decision block 1125, the prior frame, i−1, did not decodecorrectly, proceed to block 1130 to combine the symbols from bothframes. Proceed to decision block 1135 to determine if the combinedframe decoded properly. If so, use the WALSH_SPACE from the combinedframes. Initialize the decoder with WALSH_SPACE in block 1160, decodethe data control channel in block 1165, increment i in block 1170,proceed to receive the next frame i in block 1110, and repeat theprocess.

If, in decision block 1135, the combined frame did not decode properly,then proceed to block 1145. Use the previously available WALSH_SPACE. Ifthe Walsh space has not changed, then this value will be valid. If ithas changed, then, as before, the control channel will not be decodedproperly using this WALSH_SPACE value as the decoder initialization.Initialize the decoder with WALSH_SPACE in block 1160, decode the datacontrol channel in block 1165, increment i in block 1170, proceed toreceive the next frame i in block 1110, and repeat the process.Alternatively, as shown by optional block 1150 between blocks 1145 and1160 (shown in dashed outline), the mobile station can notify the basestation that the F-WICH was not received correctly, using any of themethods described above. It should be noted that alternative embodimentscould have block 1150 notify the base station that the F-WICH has notbeen received correctly anytime that the mobile station did notcorrectly receive the F-WICH.

Normally, a high reliability channel would require a great deal oftransmission power, particularly in a slow fading environment. However,the power required for a continuously transmitted F-WICH is lower. Thisis because the WALSH_SPACE is repeated, thus providing effectiveinterleaving, in the exemplary embodiment, of 40 ms. Furthermore, if themobile station is in a fade, then the carrier-to-interference (C/I) islow and the base station would not transmit to the mobile station on thepacket data channel, such as the F-PDCH. Thus, there is no need for themobile station to have the correct Walsh space information. The correctWalsh space information is only required when the channel gets better,such that the base station may select that mobile station fortransmission.

In an exemplary embodiment, an E_(b)/N_(t) of about 4 dB may be adequatefor this channel. Since the transmission rate is quite low, the requiredE_(c)/I_(or) may be about −33 dB. Such an E_(c)/I_(or) takes very littleforward link capacity to support.

The various embodiments of the present invention, some of which aredescribed above, can also be applied to handoff situations. Prior tohandoff, a base station may send a variety of messages to a mobilestation. The NGHBR_CONFIG field of the Universal Neighbor List Message(UNLM) or other Neighbor List Message indicates whether the F-PPDCCH andthe F-SPDCCH are present and their Walsh assignments are the same asthose in the current base station. For example, if the NGHBR_CONFIGfield is equal to ‘000’, then they are the same. Rather than reusing theNGHBR_CONFIG fields of the UNLM, a new field, NGHBR_CONFIG_PDCH can becreated to convey the information. In this case, a single bit couldindicate whether the F-PPDCCH and the F-SPDCCH are present and theirWalsh assignments are the same as the current base station.

When a mobile station receives a handoff message from a base station,the base station typically sends the Extended Neighbor List UpdateMessage (ENLUM) immediately after the handoff. In this message, the basestation can include the following information: whether the F-PPDCCH andthe F-SPDCCH are present, the Walsh assignments of the F-PPDCCH and theF-SPDCCH, and the F-PDCH Walsh list. Note that a single bit can be usedto represent the first two items. Two more bits can be used; the firstto indicate whether the default F-PDCH Walsh list is used, the second toindicate whether the existing (if different than the default) F-PDCHWalsh list can be used. If the default or existing F-PDCH Walsh list isnot used, then the base station must send the mobile station the F-PDCHWalsh list. As an alternative to the Extended Neighbor List UpdateMessage, the base station can send this information in a handoffmessage, such as the Handoff Direction Message.

FIG. 12 depicts a flowchart of an embodiment of this handoff method. Inblock 1210, the base station directs the mobile station to hand off. Inblock 1220, the base station sends a message indicating whether thedefault or the existing Walsh list can be used. Proceed to decisionblock 1230 to determine whether either list can be used. If so, proceedto block 1250 and proceed with the handoff, using whichever of the listsis valid. If not, proceed to block 1240 and send an updated Walsh listfor the mobile station to use. Then proceed with the handoff in block1250.

It should be noted that in all the embodiments described above, methodsteps can be interchanged without departing from the scope of theinvention.

Those of skill in the art will understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill will further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. A method of Walsh space assignment comprising: signaling, by a mobilestation, a request for transmission of Walsh space information; andsuppressing the transmission of a channel quality indicator during thesignaling.
 2. A method of Walsh space assignment comprising: signaling,by a mobile station, a request for transmission of Walsh spaceinformation; and transmitting a special value in place of a channelquality indicator during the signaling.
 3. A method for receiving aWalsh indicator channel, including a Walsh space indicator, periodicallytransmitted from a base station, comprising decoding the Walsh indicatorchannel to detect a Walsh space indicator, wherein the decoding stepcomprises decoding a time period of the Walsh indicator channel, thedecoding step further comprising: combining a second time period of theWalsh indicator channel with the first time period of the Walshindicator channel when the Walsh space indicator is not detected; anddecoding the combined time periods of the Walsh indicator channel todetect a Walsh space indicator.
 4. The method of claim 3, furthercomprising signaling the base station with a Walsh space indicatordetection acknowledgement.
 5. The method of claim 4, further comprisingsuppressing transmission from the base station in response to a negativeWalsh space indicator detection acknowledgement.
 6. The method of claim4, wherein the signaling step comprises transmitting a channel qualityindicator when the Walsh space indicator is detected.
 7. A method fordata communication, in a system including a base station transmitting acontrol channel and a periodically transmitted Walsh indicator channel,including a Walsh space indicator, comprising: decoding a first periodof the Walsh indicator channel to detect the Walsh space indicator; anddecoding a second period of the Walsh indicator channel to detect theWalsh space indicator if the Walsh space indicator is not detected inthe first period.
 8. The method of claim 7, further comprising:combining the first and second periods of the Walsh indicator channel ifthe Walsh space indicator is not detected in the first or secondperiods; and decoding the combined periods to detect the Walsh spaceindicator.
 9. The method of claim 8, further comprising selecting apreviously available Walsh space indicator if the Walsh space indicatoris not detected in the first, second, or combined periods.
 10. Themethod of claim 7, further comprising decoding the control channel usingthe Walsh space indicator as an initialization value.
 11. A method fordata communication, in a system including a base station transmitting acontrol channel and a periodically transmitted Walsh indicator channel,including a Walsh space indicator, comprising: decoding a first periodand a second period of the Walsh indicator channel to detect the Walshspace indicator; and sending a message to the base station indicatingthat the Walsh space indicator was not detected if the Walsh spaceindicator is not detected in the first period, the second period, or acombination of the first and second periods.
 12. A mobile station,communicatively coupled with a base station, the base station and themobile station containing a list of Walsh functions, one or more of theWalsh functions for use in data communication, the mobile stationcomprising: a message decoder for decoding a Walsh space indicatormessage, the Walsh space indicator message including a Walsh spaceindicator identifying a subset of the list of Walsh functions for use indata communication; and a message generator for generating a messagerequesting Walsh space information, wherein the message requesting Walshspace information is a channel quality indicator message with a uniquevalue not associated with channel quality.
 13. The mobile station ofclaim 12, wherein the Walsh space indicator is an integer k, the subsetof the list of Walsh functions being the first k Walsh functions in thelist.
 14. The mobile station of claim 12, further comprising a decoder,the decoder initialized with the Walsh space indicator prior to decodingof messages therewith.
 15. The mobile station of claim 12, wherein themessage decoder comprises: means for storing a prior message; and meansfor combining the stored prior message with a current message, thecombined messages for use in message decoding.
 16. A mobile station,communicatively coupled with a base station, the base station and themobile station containing a list of Walsh functions, one or more of theWalsh functions for use in data communication, the mobile stationcomprising: a message decoder for decoding a Walsh space indicatormessage, the Walsh space indicator message including a Walsh spaceindicator identifying a subset of the list of Walsh functions for use indata communication; and a message generator for generating a messagerequesting Walsh space information, wherein the message requesting Walshspace information is a rate indicator message with a unique value notassociated with a rate.
 17. A mobile station, communicatively coupledwith a base station, the base station and the mobile station containinga list of Walsh functions, one or more of the Walsh functions for use indata communication, the mobile station comprising: a message decoder fordecoding a Walsh space indicator message, the Walsh space indicatormessage including a Walsh space indicator identifying a subset of thelist of Walsh functions for use in data communication; and a messagegenerator for generating a message requesting Walsh space information,wherein the message requesting Walsh space information is anacknowledgement message with a unique value not associated with dataacknowledgement.
 18. A mobile station, communicatively coupled with abase station, the base station and the mobile station containing a listof Walsh functions, one or more of the Walsh functions for use in datacommunication, the mobile station comprising: a message decoder fordecoding a Walsh space indicator message, the Walsh space indicatormessage including a Walsh space indicator identifying a subset of thelist of Walsh functions for use in data communication; and a messagegenerator for generating a message requesting Walsh space information,wherein: the message decoder generates an error signal when the decodingof the Walsh space indicator message is unsuccessful; and the messagegenerator generates the message requesting Walsh space information inresponse to the error signal.
 19. A method of Walsh space assignmentcomprising: signaling, by a mobile station, a request for transmissionof Walsh space information by transmitting a unique value on a reversechannel; transmitting a channel quality indicator on the reversechannel; and transmitting Walsh space information on the forward channelwhen the channel quality indicator indicates that the channel exceeds aquality threshold.
 20. A computer program embodied on acomputer-readable medium comprising: a first set of instructions forsignaling a request for transmission of the Walsh space information; anda second set of instructions for suppressing the transmission of achannel quality indicator during signaling.
 21. A computer programembodied on a computer-readable medium comprising: a first set ofinstructions for signaling a request for transmission of the Walsh spaceinformation; and a second set of instructions for transmitting a specialvalue in place of a channel quality indicator during signaling.
 22. Anapparatus for wireless communications comprising: means for signaling arequest for transmission of the Walsh space information; and means forsuppressing the transmission of a channel quality indicator duringsignaling.
 23. An apparatus for wireless communications comprising:means for signaling a request for transmission of the Walsh spaceinformation; and means for transmitting a special value in place of achannel quality indicator during signaling.